Parallelogram lift axle suspension system with a control for axle caster adjustment

Abstract: A twin beam parallelogram-type lift axle suspension system includes a bi-directional airlift spring (79) having opposite end plates (81, 83) at either end thereof located between two parallel control arms (65, 67) wherein expansion of the air spring pivots the upper and lower control arms (65, 67) with respect to a frame bracket (61) thereby lifting an axle (75) and wheels attached thereto from engagement with the road surface. The end plates (81, 83) of the bi-directional air spring (79) move about equally in opposite directions and remain substantially parallel to one another throughout expansion and contraction of the air spring so as to about equally distribute forces of expansion of the air spring between the upper (65) and lower (67) control arms. The upper control arm (65) is pivotally connected to an axle seat by a bolt including an eccentric cam mechanism (97) which allows one to adjust the caster angle () of the axle (75) when the need arises.

Description: This application relates to auxiliary axle suspension systems for wheeled vehicles. More specifically, this application relates to auxiliary lift axle suspension systems of improved compactness and durability. BACKGROUND OF THE INVENTION In wheeled vehicle axle suspension systems, it is often desirable to have a lifting feature that lifts the wheels of the system from road engagement when their load carrying capabilities are not needed. The liftable axles are lifted when operating the wheeled vehicle in a lightly loaded or empty condition and lowered when the vehicle is loaded sufficiently to require an extra axle for safety or to conform to highway weight laws. In suspension systems for trailing axles and pusher axles, it is known that if a steerable axle is installed with the proper pitch or caster angle, the drag of the wheels will cause the axle to steer automatically in response to steering of the vehicle. This is referred to as a self-steering suspension system. It is also known in the art to provide a parallelogram arrangement of control arms or torque rods connected between a frame hanger bracket and an axle seat to maintain a substantially constant pitch of the axle and to provide lift mechanisms for such suspensions. Many devices have been used to lift axle suspensions in the past. Figures 1-2 are exemplary illustrations of such devices. Figure 1 depicts a conventional twin beam lift axle suspension which includes an air bellows 9 which angularly expands thereby raising trailing arm 21 and axle 7 attached thereto. This raising of the axle lifts the wheels of the system from engagement with the road surface. An appendage 19 is connected to trailing arm 21, and when the air bellows is expanded or contracted the trailing arm 21 is pivotally rotated about a resilient member 23 which defines a pivot point. The air bellows 9 (or airlift spring) is attached at one end 25 to the appendage 19, with the other end 27 being attached to the fixedly mounted frame hanger bracket 29. When the air bellows 9 is inflated, it reacts against the frame bracket 29 and the beam appendage 19 causing the trailing arm 21 to move relative to the bracket 29 about the pivot point defined by the resilient member 23. This expansion of the airlift spring causes the trailing arm and axle 7 to be raised and the wheels of the system to be lifted from road engagement. When the airlift spring is deflated, the axle and wheels attached thereto are lowered into engagement with the road surface. There has also been a development of another type of suspension for special applications that may be referred to as a "parallelogram" lift axle suspension. An example of this type of lift axle suspension is shown in Figures 2a and 2b. The parallelogram lift axle suspension is used primarily, but not exclusively, in steerable type lift axle suspension systems which are self-steering. The self-steering results from the liftable axle 39 being installed with the proper caster or pitch and the drag of the wheels attached to the axle causing the axle to steer automatically in response to steering of the vehicle. The reason for the popularity of the parallelogram suspension is its ability to keep the caster (i.e. angular relationship of the axle 39 relative to the ground or the horizontal) or pitch of the axle relatively constant through vertical articulation of the axle. In other words, as the axle 39 and wheels (not shown) attached thereto are lowered or raised to or from engagement with the road surface, the caster angle (or pitch) of the axle 39 remains substantially constant. The parallelogram lift axle suspension system shown in Figures 2a and 2b is typical for the industry and includes an uni-direction expanding air bellows 47, a downwardly extending frame hanger bracket 31, a lower trailing beam 33, an upper control arm 35, and an axle seat 37 connected to the axle 39. Uni-directional expansion of the air bellows 47 causes the beam 33 and arm 35 to pivot upward and lift the axle and wheels attached thereto from road engagement. Castor or pitch remains substantially constant throughout the axles raising and lowering due to the parallelogram design. The uni-directional expansion results from end plate 51 of bellows 47 being attached to fixed hanger bracket 31. Accordingly, when bellows 47 is expanded [i.e. Figure 2a], end plate 51 remains fixed while end plate 49 is moved to the left as shown in Figure 2 thereby driving beam 33 and raising the axle 39 from engagement with the road surface. The lower trailing beam 33 is pivotally attached to the frame bracket 31 at one end and pivotally attached to the axle seat 37 at the other end. The upper control arm 35 of this conventional lift axle suspension is pivotally attached to both the frame bracket 31 and the axle seat 37 at pivot points 38. The frame bracket 31, lower trailing beam 33, axle seat 37, and upper control arm 35 are all pivotally connected to form the parallelogram that allows the axle 39 to have relatively constant caster or pitch throughout its vertical articulation. The system of Figures 2a-b is exemplary of several known parallelogram lift systems. Typically, such parallelogram type suspensions provides more lift height capability than a standard twin beam lift. In the design of the parallelogram system of Figures 2a and 2b, for example, the appendage 41 is attached to the lower trailing beam or control arm 33 and an intermediate bracket 43 is pivotally attached to the appendage at a pivot point 45. The air spring or air bellows 47 is attached at one end to the intermediate bracket 43 and at the other end to the frame bracket 31. The twin beam lift system (e.g. Figure 1) lowers and raises its beams in a similar fashion, except it has no counterpart to the intermediate bracket 43 and the appendage 41 in a parallelogram suspension which allow more lift before the angular capabilities of the lift air spring 47 are exceeded. A disadvantage of the parallelogram type lift system shown in Figures 2a and 2b over that shown in Figure 1 arises from the necessity to employ added pivot point 45 to join appendage 41 to intermediate bracket 43. The addition of pivot point 45 adds a potential wear point to the suspension and thus increases maintenance requirements. This disadvantage cannot be eliminated because pivot point 45 is needed. The resulting uni-directional expansion of bellows 47, of course, gives rise to the need for a substantially large lower control arm 33 and a fairly large expansion bellows 47. One variation of the parallelogram lift axle suspension shown in Figures 2a and 2b is disclosed in UK Patent Application GB-A-2,262,722 (on which the preamble of claim 1 is based), which shows a turn buckle (not shown) adjustment mechanism, including multiple fasteners, in the upper control arm which is used to effectually adjust the length of the upper control arm and therefore adjust the caster angle of the axle through tilting of the axle seat. This allows for the caster (or pitch) of the axle to be changed as needed. For example, a truck heavily loaded in the rearward portion thereof has its rear end closer to the road surface than would an empty truck, because as additional weight is added to the rear section of the trailer, the truck is forced downward at its rear section and closer to the road surface. This changes the preferred caster of the axle and creates a need for caster adjustment. The disadvantage of the turn buckle adjustment mechanism described above is that the number of fasteners on the upper control arm is increased by about four thereby increasing the number of fasteners which must be torqued and maintained. Document GB-A-2 257 670 discloses a suspension system comprising a lower control arm attached to an axle seat and having a first end pivotally attached to a downwardly extending frame bracket by means of an eccentric cam mechanism, enabling the tracking position of the axle to be adjusted easily. It is apparent from the above that there exists a need in the art for a better means for providing a simpler caster angle adjustment mechanism in parallelogram type axle suspension that would be more cost effective, durable, and provide for decreased maintenance requirements. SUMMARY OF THE INVENTION This invention fulfills the above-described needs in the art by providing a lift axle suspension system for a wheeled vehicle, comprising the features defined in claim 1. In certain preferred embodiments of this invention, the eccentric cam is attached to a bolt wherein the bolt is slidably mounted in a slot formed in the axle seat and the means for changing the caster angle includes opposing cam contact members located on respective sides of the cam. This invention will now be described with respect to certain embodiments thereof as illustrated in the following drawings: IN THE DRAWINGS Figure 1 is a side plan, partially sectionalized view of a first prior art lift axle suspension system; Figures 2a and 2b are side plan, partially sectionalized views of a second prior art lift axle suspension system; Figures 3a and 3b are side plan, partially sectionalized views of a lift axle suspension system of this invention; Figure 4 is a cross-sectional view along A-A of system of Figures 3a and 3b; Figures 5a-5d are side plan views of the eccentric cam mechanism of the present invention; and Figures 6a and 6b are side plan views of a typical truck employing the auxiliary lift suspensions of this invention. DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS Figure 3a shows a lift axle suspension in the lifted position wherein the wheels (not shown) attached to the axle 75 are lifted out of engagement with the road surface. Figure 3b illustrates the lift axle suspension in the full rebound or lowered position where the wheels (not shown) attached to the axle 75 are in contact with the road surface. The mechanisms and controls for inflating and deflating air bellows employed as lifting and/or lowering means are well-known and conventional in the art. They consist of various air lines connecting the air from the air brake and air compression means with the bellows, and a control mechanism located in the cab of the vehicle for operation by the driver. As shown in Figures 3a and 3b, one side of the lift axle suspension according to this invention includes a downwardly extending frame bracket 61 that is attached to a frame member 63 of the vehicle. It is, of course, understood that only one-half of the suspension is shown in Figures 3a-b, the other half being located as a duplicate on the other side of the vehicle, the two halves being connected by axle 75. Upper and lower control arms 65 and 67 have first and second ends, and are of substantially the same length. The first ends of the upper and lower control arms 65 and 67 are pivotally attached to the frame bracket 61 at pivot points 69. The second ends of the upper and lower control arms are pivotally attached at pivot points 73 to an axle seat 71 which has an axle 75 mounted thereon. The upper and lower control arms 65 and 67, the frame bracket 61, and the axle seat 71 are all pivotally connected to one another thereby forming a parallelogram arrangement. In this particular type of parallelogram construction, as shown, the upper and lower control arms 65 and 67 remain substantially parallel to one another at all times. Appendages 77 are fixedly attached to each of the control arms. Bi-directional expanding and contracting air bellows 79 is located between the appendages 77 and has substantially parallel opposite end plates 81 and 83 contacting the appendages 77. The appendages 77 extend in a direction substantially perpendicular to the longitudinal axis of the air bellows 79. A coil spring, or other bi-directional expansion and contraction means may be used in place of air bellows 79 if desired. As can be seen when bi-directional air bellows 79 is inflated, it applies a substantially equal but opposite bi-directional force on the opposing appendages 77 and thus moves the control arms via both appendages 77. As shown in Figure 3a, these bi-directional forces exerted in substantially opposite directions by the air bellows (or air spring) causes the upper and lower control arms to lift, which results in axle 75 and wheels (not shown) attached thereto being lifted out of engagement with the road surface. The term "bi-directional" is used herein to mean that the bellows expands (or contracts) in two linearly substantially opposite directions thus dividing the lifting (and lowering) forces of the bellows between the upper and lower control arms. A typical air spring 85 is connected to the axle seat 71 so as to buffer axle vibration and articulation forces during road engagement of the wheels when lowered into road engagement as well as to downwardly bias the axle and wheels attached thereto and hold them appropriately into road engagement so that the suspension when so lowered carries its intended share of the vehicle load as may be required for safety or highway weight laws. The amount of air to be applied, automatically to these bellows for this purpose is well-known in the art. Air spring 85 is attached to the chassis of the vehicle by an air spring bag mount 89. The bi-directional expanding and contracting bellows 79 allows utilize smaller lifting air bellows and smaller lower control arms than would normally have to be employed, because the lifting forces of the bellows 79 are about equally distributed between the upper and lower control arms. During the lifting and lowering of the axle caused by expansion or deflation of the air bellows 79, the air bellows ends or end plates 81 and 83 remain substantially parallel to one another. Figure 4 is a cross-sectional view across line A-A shown in Figure 3b. Figure 4 illustrates the triangular cross-sectional design of the upper and lower control arms 65 and 67 which allows the bi-directional air bellows 79 to be mounted in very close proximity to the control arms. This triangular cross-sectional design provides for a more compact suspension system and allows for additional mounting space for other vehicle componentry. Because the air bellows 79 are in such close proximity to the control arms 65 and 67, the bending moment stresses in the control arms are also minimized. Such minimization of bending moment stress lengthens the life expectancy of the components therein. Figure 4 also illustrates planar surface 91 of the appendages 77 and shows the planar surface 91 of the appendages fixedly mounted to both the air bellows end plates 81 and 83, and the control arms 65 and 67. The appendages 77 may be attached to the control arms and the end plates using bolts, welds, or the like. The appendages may also be integrally formed with the control arms and/or the air spring end plates so as to simplify construction. Figure 5a is a closeup view of the axle seat end of the upper and lower control arms 65 and 67. According to the present invention the axle seat end of the upper control arm 65 is pivotally attached to the axle seat 71 with a bolt having a bolt shaft 93 and a bolt head 95. The bolt is provided with an eccentric cam 97 built into or attached to the bolt head 95. The eccentric cam 97 enables one to adjust the caster or pitch of the axle 75 as needed. As the eccentric cam head 97 is turned, the shaft 93 of the bolt moves fore and aft in a slot 92 formed in the axle seat 71. The net effect of this eccentric cam and slot arrangement is to change the caster (or pitch) of the axle 75 without changing the length of the upper control arm or any of the four links that make up the parallelogram, thus enabling one to change the caster angle by an amount , while maintaining a substantially perfect parallelogram. When the cam 97 is turned, parallel cam contact members 99, which are attached to the axle seat 71, are forced fore or aft thereby moving the axle seat 71 and altering the caster of the axle in the range indicated by the angle . The angle  illustrates how much one may adjust the caster of the axle through the cam adjustment mechanism. Optionally, the eccentric cam could be provided on the lower control arm instead of the upper control arm to achieve a similar result. The size of the cam and length of the slot dictate how much the caster of the axle may be adjusted. It is desirable in most situations to maintain the axle 75 at approximately a 5° forward pitch or 85° caster so that the vehicle will effectively self steer when driven in a forward direction. This desired caster is shown in Figure 5c where the 5° forward pitch is equivalent to an 85° caster or 85° angle with respect to the horizontal. When the need to adjust the caster angle arises, one may simply turn the bolt head 95 to simply and effectively alter the caster or pitch of the axle 75. Figure 5b shows the cam bolt 95 turned clockwise from the "zeroed up" or neutral position of Figure 5c. The result of this clockwise rotation of bolt 95 and cam 97 is that the caster changes from 85° to 82°. Figure 5d shows the bolt 95 and cam 97 having been rotated in a counterclockwise position from the position shown in Figure 5c. The result of this counterclockwise rotation is an adjusted axle caster of 88°. The size of the cam and the extent of rotation determines the amount of axle caster adjustment. The axle caster adjustment mechanism as described above would easily adapt to use with an axle having either a forward or reverse pitch. The caster (or pitch) of the axle 75 remains substantially constant during raising and lowering of the axle 75 because of the parallelogram nature of the lift axle suspension (the control arms remain substantially parallel). The above discussed caster adjustment mechanism is a significant improvement over that of the prior art in that it is simpler, requires less maintenance, requires fewer parts, does not cause a loss of paralleloism, and is easier to install and adjust. The axle 75 is connected to the axle seat 71 and is adapted to receive one or more wheels at both ends thereof. The axle 75 may be connected to the axle seat 71 using bolts, welds or any other suitable means; the biasing air springs 85 are also attached to the vehicle chassis side rail frame members 63 via mount 89. Figures 6a and 6b illustrate a wheeled vehicle 107 (e.g. a semi-trailer or rear of a heavy duty truck) equipped with the suspension (e.g. Figures 3-5) of the present invention. The wheeled vehicle 107 includes at least two non-liftable wheel bearing suspensions and wheels 109 attached thereto. These non-liftable wheel bearing suspensions provide the primary means of support for road engagement of the vehicle. The wheeled vehicle is also equipped with the lift axle suspension system of an embodiment of the present invention and wheels 111 attached thereto. Figures 6a and 6b illustrate the wheels (111 and 109) of both the lift axle suspension system and the fixed non-liftable axle suspension system mounted on the wheeled vehicle 107. Figure 6a illustrates the lift axle suspension and wheels 111 attached thereto in the raised position with the wheels 111 lifted out of engagement with the road surface 113. Figure 6b illustrates the lift axle suspension system of the present invention in the lowered position with the wheels 111 engaged with the road surface. The wheels 111 shown in Figures 6a and 6b are connected to the axle 75 shown and described above. When bi-directional air bellows 79 is inflated, the upper and lower control arms are caused to lift which results in the wheels 111 being lifted out of engagement with the road surface. Likewise, when bellows 79 is deflated, the control arms are caused to lower due to the force of air spring 85, resulting in the wheels 111 being engaged with the road surface as shown in Figure 6b. It will be clear to one skilled in the art that the various elements which make up the lift axle suspension systems outlined herein may be connected to one another in tandem form, if desired, using any suitable means, and may be made of any suitable materials. Once given the above disclosure many other features, modifications and improvements will become apparent to the skilled artisan. Such other features, modifications and improvements are therefore considered to be a part of this invention, the scope of which is to be determined by the following claims:

Claims: A lift axle suspension system for a wheeled vehicle, comprising: a downwardly extending frame bracket (61) attached to the vehicle frame; upper and lower control arms (65, 67) each having a first end pivotally attached to the frame bracket (61) at pivot points (69) and a second end pivotally attached at pivot points (73) to an axle seat (71) which has an axle (75) mounted thereon; said frame bracket (61), upper and lower control arm (65, 67) and axle seat (71) forming a parallelogram arrangement; expansion means (79) acting on at least one of said upper and lower control arms (65, 67) for pivoting it with respect to said bracket (61) whereby raising and lowering the axle seat (71) ; one of said control arms (65) including means for changing the caster angle () of said axle (75) characterised in that said expansion means (79) are bi-directional expansion means (79) connected between said upper and lower control arms (65, 67), and in that one of said control arms (65) is pivotally connected to said axle seat (71) by an eccentric cam mechanism (97) enabling the caster angle () of the axle (75) to be adjusted without changing the length of the control arm (65). A system as claimed in claim 1, characterised in that wheels are attached to said axle (75). A system as claimed in claim 1, characterised in that said eccentric cam (97) is attached to a bolt (93) wherein the bolt (93) is slidably mounted in a slot formed in the axle seat (71). A system as claimed in claim 3, characterised in that the means for changing the caster angle () further comprises opposing cam contact members (99) located on opposite sides of said cam (97). A system as claimed in claim 1, characterised in that said bi-directional expansion means (79) has first and second ends defined by a plate means (81, 83) at each end, said plate means (81, 83) move in opposite directions and remain substantially parallel to one another when said expansion means (79) expands and contracts. A system of claim 5, characterised in that said expansion means includes an air bellows (79), and said plate means (81, 83) move about equally in said opposite directions so as to about equally distribute expansion forces of said expansion means between said upper and lower control arms (65, 67). A system as claimed in any one of the claims from 1 to 6, characterised in that said upper and lower control arm (65, 67) are of substantially the same length.

Inventors: GOTTSCHALK MICHAEL J, KEELER MICHAEL J, GOTTSCHALK, MICHAEL J., KEELER, MICHAEL J.
Applicants: BOLER CO, THE BOLER COMPANY.
Application year: 1994
Main classification: B62D17
IPC codes: B62D17, B62D61, B60G11